Refractory lined ducts and coating for use therewith

ABSTRACT

The present invention is directed to ceramic fiber insulation and related products and methods. A coating that is capable of being brushed and/or sprayed lightly as a liquid onto vacuum-formed ceramic fiber insulation for use at high temperatures is also provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to ceramic fiber insulation, andmore particularly to methods and coatings for use with the same.

2. Description of Related Art

In many industrial applications it is necessary that conduits or ductsbe provided for interconnection of various types of apparatus whichrequire the routing of hot atmospheres or gases of many chemicalcompositions from one component to another. In most of theseenvironments, the hot gases exhibit not only corrosive characteristicswhich will adversely affect conventional metallic conduits, but are alsocaused to flow at relatively high velocities. The relatively high gasflow velocity frequently encountered results in further adverse effectsof frictional wearing and erosion of the interior of metallic ducts orother types of ductwork including but not limited to the increasedlikelihood of chemical corrosion. The relatively high temperatures alsohave a substantial adverse effect on the metal conduit such asdecreasing structural strength and presenting a safety hazard to workerswho may need to be in close proximity.

One technique heretofore utilized to meet the requirements of thishighly adverse operational environment has been to line metallic orsteel ducts with a castable refractory material. A disadvantage of theducts having the castable refractory liner is that such refractories arenot thermally efficient and as a consequence, the metal ducts which arelined with such materials must be made so as to develop greaterstructural strength to support the weight of the castable refractorythat is required in most cases to meet the operational requirements.

There has also been an attempt to form ducts capable of withstanding theoperational requirements of transmission of hot gases by lining metalconduits with a soft ceramic fiber material. The soft ceramic fibermaterial, as its name implies, does not exhibit the desired resistancecharacteristics to erosion by the relatively high gas velocities thatare encountered. In an effort to meet the erosion effect, there havebeen attempts to also coat the interior surface of these liners with alayer of suitable material to attempt to rigidify the interior surfacelayers. These attempts have also not proven to be sufficientlysuccessful as the rigidifying surface material will eventually crack andpeel off and expose soft ceramic fibers to the point where the linerswill erode and eventually become unusable, thus requiring replacement.

Another disadvantage of either the castable refractory liners or thesoft ceramic fiber lining is the technique of obtaining the attachmentor positioning of the liner within the metal conduit. The usualtechniques require first securing of anchors to the interior of themetal duct. The refractory material is then either mechanically securedor it is formed directly onto those anchors such as by spraying ormolding. Similarly, the soft ceramic fiber linings have been applied tothe interior of the metal conduits by use of anchors which are firstsecured to the interior of the metal conduit.

Another attempt to meet the problems has been the formation of a vacuumcast sleeve or liner which is then subsequently assembled with a metalduct. This technique is not particularly advantageous in that itrequires assembly at the operational site where the duct will beutilized. This technique increases the cost of installation.

In order to meet fire codes in terms of fireproof and fire resistanceprotection, insulation products must either have substantial mass or beendothermic in nature. Therefore, many insulation products must betreated or fabricated in such a way so as to give them such properties.Many endothermic materials are known. However, there are still problemsassociated with such materials and it would be desirable to have amaterial that is advantageous in terms of its end use properties and itsease of manufacture.

SUMMARY OF THE INVENTION

In accordance with these and other objectives, the present invention isdirected to ceramic fiber insulation and related products and methods.The present invention further is directed to a ceramic coating that iscapable of being brushed and/or sprayed lightly as a liquid ontovacuum-formed ceramic fiber insulation for use at high temperatures.

In a preferred embodiment, the instant invention provides a method formaking refractory linings and insulation products wherein a ceramicfiber sleeve is positioned in and retained without the need forexpansion joints and, in most applications, without utilization ofmechanical attachment anchors, however the instant invention alsocontemplates the use of expansion joints and anchors as well. Preferredembodiments of the instant invention also provide ceramic fiber liningscapable of handling gases of relatively high temperatures.

The instant invention also provides a ceramic fiber lined ductcomprising a vacuum-formed ceramic fiber liner that has been treatedwith a coating affixed to a metal jacket.

In another preferred embodiment, the instant invention provides a methodof making a duct capable of handling gases of relatively hightemperatures and also having fire resistant, erosion resistant, andcorrosion resistant properties fabricated by first forming a ceramicfiber sleeve and, while the sleeve is in a wet or hydrated state,positioning the sleeve within a metal tube and thereafter subjecting theassembly to a drying operation to remove moisture from the ceramic fibersleeve. This method results in the sleeve and metal tube beingmechanically and adhesively secured together into assembledrelationship.

In another preferred embodiment, the instant invention provides a methodof vacuum-forming a ceramic fiber insulation or lining conforming to thesize and shape of a particular fitting or commercial heating componentand positioning it within a metal jacket similarly to a ceramic fibersleeve within a metal tube.

In another preferred embodiment, the instant invention provides a“clamshell” method for making ceramic fiber-lined metal-jacketedfittings or ducts of complex shapes which cannot be made with a singlevacuum-forming operation. This involves forming sections or halfsections of such a fitting or duct and combining them so as to make onecomplete fitting.

In another preferred embodiment, the instant invention provides a methodfor making refractory linings and insulation products wherein materialssuch as, but not limited to, mineral wool and/or graphite felt can beused in place of or in addition to ceramic fiber within the metal jacketof a duct, fitting or commercial heating component.

The instant invention also provides a refractory lining comprising avacuum-formed ceramic fiber liner that has been treated with a coating.In a preferred embodiment, the instant invention provides a method ofincreasing fire resistance, thermal resistance, erosion resistance, andcorrosion resistance of a vacuum-formed ceramic fiber lining comprisingtreating said ceramic fiber lining with a coating on a surface of saidceramic fiber insulation, wherein said coating renders said duct capableof being used at temperatures from about 2300° F. to about 3000° F.

In addition to the above applications, the coating's fire resistance, asopposed to merely heat resistance, as well as the coating's erosionresistant and corrosion resistant properties, make the present coating adesirable coating for vacuum-formed ceramic fiber products. In ibiscase, as in the above applications, the coating would preferably bebrushed and/or sprayed lightly onto the hot face of ceramic fiberinsulation, whether or not the insulation contains an outer steeljacket.

Additional objects, features and advantages of the invention will be setforth in the description which follows, and in part, will be obviousfrom the description, or may be learned by practice of the invention.The objects, features and advantages of the invention may be realizedand obtained by means of the instrumentalities and combinationparticularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate a presently preferred embodimentof the invention, and, together with the general description given aboveand the detailed description of the preferred embodiment given below,serve to explain the principles of the invention.

FIG. 1 is an elevational view of a duct formed in accordance with themethod of this invention with portions of the elements removed forclarity of illustration.

FIG. 2 is an elevational view of a ceramic fiber sleeve formed by avacuum process onto a die.

FIG. 3 is a diagrammatic illustration of the process of assembly of theceramic sleeve in a wet form into a metal tube.

FIG. 4 is an elevational view of a section of conduit formed inaccordance with the method of this invention and having multiplerefractory liners.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

In a preferred embodiment, the present invention relates tohigh-temperature vacuum-formed ceramic fiber insulation, as well as to acoating which can be applied to ceramic fiber products so as to makethem more resistant to erosion and corrosion caused by extreme velocityin high-temperature airflow within ductwork and by particulate matter inthat airflow. The invention further relates to improvements inrefractory liners for ducts or conduits, and particularly to ducts orconduits having a ceramic fiber liner functioning as a refractory toaccommodate the corrosive and abrasive characteristics of hot gasesdesigned to be routed through such conduits or ducts. It further relatesin particular to a method for making of a duct having a refractory linerof ceramic fiber.

As used herein a duct is a metallic enclosed vessel or conveyanceincluding, but not limited to, a pipe, tube, or channel.

Suitable high emissivity coatings are disclosed, for example, in U.S.Pat. No. 5,296,288, the content of which is incorporated herein byreference in its entirety. For example, a coating of the instantinvention generally comprises a mixture of: silicon oxides such assilicon dioxide powder and colloidal silicon dioxide; water, preferablyde-ionized; one or more emissivity agents; and optional organic elementsas additives to extend shelf life.

An emissivity agent is an agent which radiates heat into the duct andaway from the lining. Typical emissivity agents of the instant inventioninclude, but are not limited to polyborides such as silicon hexaborideor silicon tetraaboride, silicon carbide, molybdenum disilicide,tungsten disilicide and zirconium diboride.

In one preferred embodiment the coating comprises a mixture of silicondioxide power in an amount of from about 23.0 to about 44.0 wt %;collodial silicon dioxide in an amount from about 25.0 to about 45.0 wt%, water in an amount from about 19.0 to about 39.0 wt %, and anemissivity agent preferably is in the form of a powder. The protectivecoating can have a solids content of from about 40 to about 60 wt %.

The present coating is especially resistant to hostile environmentalconditions, such as air velocity, temperature, acidity, water vapor orsteam, etc. The coating is suitable for withstanding the sametemperature range as the ceramic fiber lining itself, for example about2300° F. to about 3000° F.

The protective coating can easily be prepared, for example, by preparinga slurry of the components of the coating, and then ball milling theslurry to provide a uniform solid dispersion which is then further mixedtogether.

It has unexpectedly been found that the coating according to the presentinvention is highly resistant to fire. Accordingly, in a preferredembodiment, the instant invention provides a vacuum-formed ceramic fiberinsulation or liner treated with a coating of the present invention. Inthis way, the treated ceramic fiber insulation or liner is resistant toerosion caused by air velocity, to particulate matter in such an airstream, to corrosion caused by acid, moisture, fire and extreme heat.

The instant coating may be applied to a ceramic fiber lining orinsulation by any method commonly employed in the art, such as brushingor spraying.

The present coating is particularly advantageous for use with: (1)ductwork that is adapted for high velocity airstreams, (2) ductwork thatis used for airstreams having particulate matter; (3) ductwork thatregularly is exposed to airstreams having an acidic content thereinand/or (4) ductwork that accepts airstreams having a high moisturecontent. Because of its inherent fire and heat resistant properties, thepresent coating may also be used for high-temperature applications suchas those at or above about 2300° F. Often it may be cost-effective toapply the coating as a heat barrier, thereby permitting a reduction ofthe wall thickness of the insulating ceramic fiber. In the case ofsteel-jacketed ceramic fiber products such as Danser Inc.'s commerciallyavailable VACUDUCT® product, the coating's heat barrier may also permita reduction in the diameter and amount of the steel necessary to enclosethe insulating layer of ceramic fiber. For example, the thickness couldbe reduced by about 5-50%.

Particularly challenging duct environments may require two applicationsof the coating. First a dilute application, for example, from about 10%to about 90% strength, and more preferably from about 10% to about 15%strength) may be applied so as to maximize absorption into therelatively porous density of vacuum-formed ceramic fiber, which may beapproximately 17 lbs./cu. ft. This dilute application can thenadvantageously be followed by a full-strength application to maximizethe impervious nature of the barrier to air velocity, particulatematter, acid, moisture and heat.

The instant coating is suitably applied to materials, such as refractoryliners or refractory liners with passive fire resistance, due to itshigh emissivity. The present coating's high emissivity qualities aregreatly advantageous over prior endothermic materials. Coated ceramicfiber insulation according to the present invention is generally capableof meeting appropriate ASTM, NFPA and UL fire prevention standards.

A coating composition for coating the interior of ceramic materials suchas ceramic fiber-lined ducts of the present invention act to directthermal energy toward a load in the duct wherein the duct reaches atemperature of above about 1100° C., thereby increasing the thermalefficiency and also the fire resistance of the interior of the ductwork.

In a preferred embodiment, the instant invention provideshigh-temperature vacuum-formed ceramic fiber insulation for ductwork.U.S. Pat. No. 5,078,822, the content of which is incorporated herein byreference in its entirety, discloses a refractory lined duct, fitting,or component having a sheet metal outer jacket or “skin” lined on theinside with a ceramic fiber matrix bonded with binder materials forminga refractory lining of predetermined shape, thickness, and thermalcharacteristics. This duct's refractory lining is held in fixed,retained relationship with the exterior sheet metal jacket solely byfrictional and adhesive forces inherent in the art of the invention.

A method for making the duct, fitting, or component includes the stepsof vacuum-forming a refractory inner lining, conforming to the shape ofthe sheet metal outer jacket, from a slurry of ceramic fibers and bindermaterials onto a forming die, inserting the ceramic fiber lining whilein a hydrated state into the sheet metal supporting jacket or casing ofcomplementary shape and size such that adjacent surfaces of the jacketand sleeve are in contacting engagement, and then drying the assembly toremove the water resulting in the formation of a hard, solid-structurerefractory liner that is fixed in the tube solely through frictional andadhesive forces inherent in the art of the invention. A modified duct,or fitting, formed by the same methodology includes a compositerefractory liner formed from a plurality of tubular liners that eachhave their own respective structural, physical and thermalcharacteristics.

The present invention further provides refractory lined ducts, fittingsor components having sheet metal jackets or casings lined with a ceramicfiber matrix bonded with binder material forming refractory liners ofpredetermined thickness and thermal characteristics. For example, linerthicknesses range preferably from about 1 to about 8 inches and morepreferably from about 2 to about four inches with thermalcharacteristics when dry of a low density insulation which is also lowin thermal conductivity and highly resistant to thermal shock. The ducthas the refractory liner held in fixed, retained relationship with itsouter metal jacket solely by frictional forces and adhesive bonding bythe binder material. A modified duct or fitting formed by the samemethods includes a composite refractory liner formed from a plurality oftubular liners that each have their own respective structural, physicaland thermal characteristics. It is also possible to render suchmaterials erosion resistant, corrosion resistant, and fire resistant oreven fireproof by applying a coating such as corrosion resistantcoatings and/or coatings of the instant invention.

In accordance with this invention, there are also provided methods formaking the instant refractory lined ducts, fittings or components. In apreferred embodiment, a ceramic fiber inner lining is positioned in andretained within a metal jacket or casing. In accordance with thispreferred embodiment, a duct capable of handling gases of relativelyhigh temperatures, for example, 2300° F., and also having corrosiveproperties, is fabricated by first forming of a ceramic fiber innerlining and, while the lining is in a wet or hydrated state, positioningthe lining within the metal jacket and thereafter subjecting theassembly to a drying operation to remove moisture from the ceramic fiberlining. This method results in the lining and metal jacket beingmechanically and adhesively secured together into an assembledrelationship.

The ceramic fiber lining can be formed, for example, by well-knownoperations for vacuum-forming of such articles through placement andforming of the ceramic fibers onto a forming die. The ceramic fibers areformed in a layer on the die to form a fiber lining having an outsidediameter or shape that is at least equal to, if not slightly larger thanthe interior diameter or chamber of the metal jacket or casing intowhich the lining is to be placed. While in a wet condition, thedie-supported fiber lining is inserted into the metal jacket and the dieis removed either at a point in time where the ceramic fiber lining ispartially inserted within the jacket or when it is fully inserted. Afterthe die is removed from the ceramic fiber lining, the assembled metaljacket and ceramic lining are placed in an oven wherein the elevatedtemperature of the oven and airflow is sufficient to effect evaporationof the water from the ceramic fiber lining.

Preferably, a method for making the instant duct, fitting, or componentcomprises the steps of vacuum-forming a refractory inner lining from aslurry of ceramic fibers and binder materials onto a forming die,inserting the ceramic fiber lining while in a hydrated state into thesheet metal supporting jacket or casing of complementary shape and sizesuch that adjacent surfaces of the jacket and sleeve are in contactingengagement and then drying the assembly to remove the water resulting informing of a hard, solid structure refractory liner that is fixed in thetube solely through frictional and adhesive forces inherent in the artof the invention.

The ceramic fiber lining is of a size such that when it has been dried,it will mechanically engage with the interior surface of the metaljacket and be at least partially retained therein through frictional andadhesive forces resisting relative axial displacement. The instantinvention is particularly suited for predetermined shapes,configurations and sizes of metal jacketed ceramic fiber lined ducts,fittings or components in sizes, for example, ranging from an innerdiameter of two inches to an outer diameter of eight feet.

In accordance with another aspect of this invention, a conduit assemblyor fitting having multiple ceramic fiber liners is provided throughsequential formation and insertion of two or more ceramic fiber linersinto a metal jacket or casing. This aspect of the invention enables aceramic fiber liner adapted to lower temperature applications to befirst placed within the conduit and then a second ceramic fiber lineradapted for higher temperature applications inserted and secured in asimilar manner.

In a preferred embodiment, the invention provides a method of makingrefractory lined ducts having an elongated, structurally supporting tubeand a ceramic liner carried on an interior wall of the duct comprisingforming a sleeve of ceramic fiber and binder materials on a structurallysupportive die in a hydrated state by vacuum-forming wherein said sleevehas an external wall of a configuration that is geometrically anddimensionally complemental to the interior wall of the supporting ductto form an interference fit therewith effective in mechanicallyretaining said sleeve and duct in fixed interengagement; inserting thesleeve, while in a hydrated state and on the die, coaxially into thesupporting tube and after insertion, removing the die from the sleeve;and drying the sleeve while said sleeve is maintained in fixed positionwithin the supporting tube to remove substantially all liquid resultingin solidification of the sleeve in a frictionally and adhesivelyretained relationship with the supporting tube.

A preferred embodiment is illustrated in FIG. 1, wherein a refractorylined duct 10 embodying this invention and formed in accordance with themethod is shown with portions broken away for clarity of illustration.The duct 10 includes a structurally supporting tube 11 and a refractoryliner 12. The tube 11 is formed from a suitable material for theparticular installation and may most commonly be formed of sheet steel.The size of the duct 10 is also dependent upon the particularinstallation for which the duct is designed as is the diameter. As anexample, duct embodying this invention may have a nominal diameter inthe range of about 2 to about 100 inches, more preferably about 8 toabout 50 inches with the liner itself having a thickness of the order of3 inches. Duct of this type frequently is required in installationswhere there are large volumes of gaseous materials that must betransported from one location to another, and accordingly, large-sizeducts are preferred to reduce velocities while maintaining sufficientcapacity to handle the volume of gas.

The supporting tube 11 which is indicated to be fabricated of sheetsteel may be of a type that is formed by spiral winding techniques ofelongated strips of steel with the adjacent edges being mechanicallyinterlocked. FIG. 1 does not illustrate specifics of detail of thestructure of the tube 11 as that does not form a part of the inventionand is dependent upon a particular design. However, the tubes 11 aregenerally provided with end flanges 13 which provide a means formechanically interconnecting a number of such ducts in serial alignment.These flanges are generally drilled to accommodate fastening bolts.Again, the technique of interconnecting adjacent duct in end-to-endrelationship is a matter of mechanical design and is of a type selectedto be appropriate for a particular installation and the details are nota part of this invention.

In accordance with this invention, the refractory liner 12 is retainedin position within the interior of the supporting tube 11 through acombination of frictional and adhesive forces as between the contactingwall surfaces of the liner and the tube. As can be seen in FIG. 1, theliner 12 has an inner wall surface 14 which is termed “The Hot Face” andan outer wall surface 15 which is termed “The Cold Face”. One of thefunctions of the refractory liner 12 is to provide thermal insulationand thus have a characteristically low thermal conductivity such thatthe cold face will not exceed predetermined temperatures for aparticular application. This is advantageous to reduce the mechanicalstresses that must be accommodated by the supporting tube II as well asenhancing safety in the environment as it concerns workers who mustoperate in the processing installation in which such duct may beinstalled.

In accordance with this invention, the refractory liner 12 is formedfrom ceramic fibers which are held in a matrix by suitable binders. Theceramic fibers that are particularly useful for a refractory liner ofthis type and for high-temperature installations comprise a combinationof alumina-silica fibers and aluminum oxide fibers. These fibers whichare of small cross-sectional shape are held in a matrix by means ofbinders which may include combinations of colloidal silica binders andcationic starch binders. These materials are mixed in a slurrycomposition which, through a vacuum-forming process, can be fabricatedinto a tubular shape such as the illustrative refractory liner, or intovirtually any shape complementary to an outer steel jacket or casing.The specific materials, their proportions in the composition, are knownin the art and the specifics are not deemed of importance to theinvention other than to note that the materials are selected inaccordance with known techniques to form a refractory which will havethe desired thermal and structural characteristics.

In another preferred embodiment, the instant invention provides for theaddition of a plasticizing agent in the ceramic slurry mix to reducebrittleness of individual ceramic fibers in the finished product therebyreducing erosion and thermal shock of the finished product when it is inoperation.

In another preferred embodiment, the instant invention provides for theaddition of a de-wetting agent in the ceramic slurry mix to acceleratedrying of the finished product after it has been removed from the die.

Vacuum-forming of a tubular liner such as that which is illustrated isconventionally accomplished by vacuum-forming techniques with theceramic fibers and binder being collected on an elongated tubular die.This forming technique is diagrammatically illustrated in FIG. 2 wherean elongated die 16 is shown with a quantity of the ceramic fibers andbinder collected on its exterior and thus forming an elongated tube. Inthe initial forming stages, the ceramic fiber and binder matrix is in ahighly hydrated state, although it will be sufficiently compacted withthe binder material functioning to adhesively secure the fibers in astructurally self-supporting shape. The refractory liner at this stagecan be handled and moved for performance of other operations to completeits fabrication. Such tubular refractories are utilized in otherapplications than that of the invention and, for such purposes, thearticle subsequent to the initial vacuum-forming operation is subjectedto a drying operation such as by placing the article in a conventionaloven and circulating air for evaporation of the moisture which ispredominantly water in another preferred embodiment, the lining,subsequent to the initial vacuum-forming operation, is subjected to adrying operation in a microwave oven wherein penetrating microwaveenergy and airflow are sufficient for evaporation of moisture. In eithertype of drying environment the temperatures and drying times aredependent upon the particular characteristics of the fiber lining as toits physical size and moisture content. The article as thus formed inaccordance with prior art practices is a structurally solid article thatcan be mechanically placed and secured in specific installations.

However, in accordance with the method of invention for forming the ductembodying this invention, the tubular refractory liner 12 while in a wethydrated state is first positioned within the interior of the supportingtube II prior to being subjected to a drying operation. Depending uponthe state or degree of hydration of the liner, it may be advantageous todry the liner to an extent where it will have adequate structuralintegrity to enable its assembly with the tube. To form a duct 10embodying this invention, the refractory liner 12 is formed with anexterior diameter that is at least equal to or advantageously slightlylarger than the inside diameter of the supporting tube 11. For example,in the case of a supporting tube 11 having a diameter in the range ofabout 2 to abut 100 inches, more preferably about 8 to about 50 inches,the exterior diameter of the liner 12 as fabricated by thevacuum-forming process may be one-fourth inch larger to better assurethat there will be a mechanical engagement as between the liner and tubeto result in the desired frictional forces for retaining the linerwithin the tube. Assembly of a vacuum-formed liner with the tube 11 isdiagrammatically illustrated in FIG. 3. While the refractory liner 12 isin a hydrated state and still retained on the forming die 16, it can beeasily lifted and slid axially into the upper open end of the tube 11.The tube 11 would be supported on a transporting plate or other carrierdevice and the liner 12 as it slides down into the tube 11 would alsocome to rest on that supporting plate. As the liner 12 is slid into thetube, excess refractory material may be skinned or shaved off from theexterior surfaces or realigned onto the surface forming a continuouscontacting surface engagement with the interior of the supporting tube11. A refractory liner in a hydrated state does not have a smoothsurface as the material has a tendency to flow to a certain degree andthis is illustrated in FIG. 2 by the rough surface conformation. Whenthe liner is at least partially inserted within the tube, the formingdie 16, may be removed. This may be accomplished by mechanical rotationof the die which will break the surfaces loose and enable the die to bewithdrawn. Once the die has been withdrawn, the hydrated liner willcontinue sliding down into the tube until it comes to rest on the bottomsupporting plate.

Once the hydrated liner is fully positioned within the tube, theassembly may then be subjected to a drying procedure. This dryingprocedure follows that previously described in connection with formingof refractory articles of a more conventional nature. Such a procedureas indicated comprises placing the article into an oven which is at asufficiently elevated temperature, or utilizes microwave energy, so asto cause evaporation of the water in the liner. Air is circulated aroundthe articles to aid in removal of the water vapor and thereby hasten thedrying process. A drying apparatus is not shown as such is well-known inthe art as are the operating techniques as to temperature and airflow.The operation does continue until the water is evaporated at which timethe refractory material is fully solidified. This process also completesforming of the inter-fit of the liner to the interior of the tube toresult in generation of frictional and adhesive forces which prevent theremoval of the liner from the supporting tube. Thus, in accordance withthis invention, a duct 10 having a refractory liner is provided whichdoes not require the use of any other mechanical means for securing therefractory liner within the interior of the tube.

A modified duct 20 also fabricated in accordance with the method of thisinvention and thus embodying the advantageous structural arrangement isshown in FIG. 4. This duct also includes a structurally supporting tube21 and a refractory liner designated generally by the numeral 22.However, in this modification, the liner 22 comprises a plurality oftubular refractory liners with two ceramic fiber liners 23 and 24 shownwhich are disposed in coaxial relationship to each other and to thesupporting tube 21. Utilizing two liners 23 and 24 to form a compositerefractory liner 22 permits each of the liners to be fabricated fromdifferent combinations of materials. By appropriately proportioning thetypes of ceramic fibers that are selected and the binder materials, itis possible for a liner of predetermined thickness to be formed havingdifferent physical and thermal characteristics. One objective of this isthat the inner liner 23 of such a composite structure may advantageouslybe formed from ceramic fiber materials and binders such that it willhave relatively less thermal shrinkage at high temperatures. The secondliner 24 may then be formed from the ceramic fiber materials and binderswith the resulting liner having a characteristically higher shrinkage athigh temperatures. This dual liner construction thus permits a lowerfabricating cost as the inner liner having a relatively lower thermalshrinkage is relatively more expensive as compared to the outer liner.

Other factors may also be considered in a combination of two liners toachieve particular physical and thermal objectives. For example, inanother preferred embodiment, the instant invention provides a methodfor making refractory linings and insulation products wherein materialssuch as, but not limited to, mineral wool and/or graphite felt can beused in place of or in addition to ceramic fiber within the metal jacketof a duct, fitting or commercial heating component.

Assembly of the dual liners 23 and 24 with the supporting tube may beeffected in substantially the same manner as described with respect tothe assembly shown in FIG. 3. A first liner 24 is placed within thesupporting tube 21 with its die then being removed. A 10 second orinnermost liner 23 may then be similarly placed within the outer linerin the same manner and its respective forming die then removed. Theassembled liners and supporting tube may then be subjected to anappropriate drying procedure to remove the water. With the water beingremoved, the two liners then maintain their respective coaxial alignedpositions through frictional and adhesive forces as is the assemblyretained within the supporting tube.

It will be understood that the dimensions given for the illustrativeduct are for purposes of example and that the duct may be fabricated inany desired size and configuration. It will also be understood that theillustrative dimensional thickness of the refractory liner is also forpurposes of example and its thickness may be varied depending upon theparticular installation in which the duct will be placed. Also, thespecific ceramic fiber materials and binders will be selected on thebasis of the structural and thermal characteristics desired for theparticular duct.

In the present invention, there is also provided high-temperaturevacuum-formed ceramic fiber insulation, as well as a coating used forpassive fire protection applications such as in commercial construction,manufactured products, transportation, and industrial constructionmarket segments. These materials can be used, for example, to controlthe spread of flames and to limit an increase in temperature in order toprevent or contain the outbreak of fire. Potential applications includefireproof storage cabinets and safes, hazardous material storage andtransportation containers, ventilation and grease ducts, electrical andtelecommunication conduits, and cable trays.

It will be readily apparent that a novel and particularly advantageousrefractory duct, fitting or industrial beating component is provided bythis invention. It will also be readily apparent that the method of itsfabrication results in economy of assembly and produces a unitarystructure wherein the refractory liner and supporting metal jacket areretained in mechanical inter-engagement.

Additional advantages, features and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, and representativedevices, shown and described herein. Accordingly, various modificationsmay be made without departing from the spirit or scope of the generalinventive concept as defined by the appended claims and theirequivalents.

As used herein and in the following claims, articles such as “the”, “a”and “an” can connote the singular or plural.

All documents referred to herein are specifically incorporated herein byreference in their entireties.

1-3. (canceled)
 4. A ceramic fiber lined duct comprising a vacuum-formedceramic fiber liner that has been treated with a coating affixed to ametal jacket.
 5. A vacuum-formed ceramic fiber lined duct according toclaim 4, wherein said coating comprises a mixture of: silicon dioxidepower; collodial silicon dioxide; water; and an emissivity agent.
 6. Avacuum-formed ceramic fiber lined duct according to claim 4, whereinsaid coating comprises a mixture of: silicon dioxide power in an amountof from about 23.0 to about 44.0 wt %; colloidal silicon dioxide in anamount from about 25.0 to about 45.0 wt %; water in an amount from about19.0 to about 39.0 wt %; and an emissivity agent selected from the groupconsisitng of silicon hexaboride, silicon tetraaboride, silicon carbide,molybdenum disilicide, tungsten disilicide and zirconium diboride. 7-13.(canceled)
 14. A refractory lined duct comprising an elongated,structurally supporting tube and a liner carried on an interior wall ofthe duct prepared by the process comprising: a) forming a sleeve on astructurally supportive die in a hydrated state by vacuum-formingwherein said sleeve has an external wall of a configuration that isgeometrically and dimensionally complemental to the interior wall of thesupporting tube to form an interference fit therewith effective inmechanically retaining said sleeve and tube in fixed interengagement; b)inserting the sleeve, while in a hydrated state and on the die,coaxially into the supporting tube and after insertion, removing the diefrom the sleeve; and c) drying the sleeve while said sleeve ismaintained in fixed position within the supporting tube to removesubstantially all liquid resulting in solidification of the sleeve in africtionally and adhesively retained relationship with the supportingtube; wherein said method further comprises treating said sleeve with acoating, wherein said coating comprises a mixture of: silicon dioxidepowder; collodial silicon dioxide; water; and an emissivity agent.